.TH std::hash,std::hash,std::hash, 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::hash,std::hash,std::hash, \- std::hash,std::hash,std::hash,

.SH Synopsis

   Defined in header <string_view>
   template<> struct hash<std::string_view>;     \fI(since C++17)\fP
   template<> struct hash<std::wstring_view>;    \fI(since C++17)\fP
   template<> struct hash<std::u8string_view>;   \fI(since C++20)\fP
   template<> struct hash<std::u16string_view>;  \fI(since C++17)\fP
   template<> struct hash<std::u32string_view>;  \fI(since C++17)\fP

   Template specializations of std::hash for the various view classes for hashing
   views.

   These hashes equal the hashes of corresponding std::basic_string classes: If S is
   one of the standard basic_string types, SV is the corresponding string view type,
   and s is an object of type S, then std::hash<S>()(s) == std::hash<SV>()(SV(s)).

.SH Example


// Run this code

 #include <iostream>
 #include <string_view>
 #include <unordered_set>
 using namespace std::literals;

 int main()
 {
     std::cout << "\\"A\\"   #: " << std::hash<std::string_view>{}("A"sv) << '\\n';
     std::cout << "L\\"B\\"  #: " << std::hash<std::wstring_view>{}(L"B"sv) << '\\n';
     std::cout << "u8\\"C\\" #: " << std::hash<std::u8string_view>{}(u8"C"sv) << '\\n';
     std::cout << "u\\"D\\"  #: " << std::hash<std::u16string_view>{}(u"D"sv) << '\\n';
     std::cout << "U\\"E\\"  #: " << std::hash<std::u32string_view>{}(U"E"sv) << '\\n';

     // std::hash for string_view family makes it possible to keep these view-types
     // in unordered_* associative containers, such as unordered_set. But ensure
     // the lifespan of referenced strings is no less than lifespan of the container,
     // i.e. no dangling references occurred.

     std::unordered_set stars{"Rigel"sv, "Capella"sv, "Vega"sv, "Arcturus"sv};

     for (std::string_view const& s : stars)
         std::cout << s << ' ';
     std::cout << '\\n';
 }

.SH Possible output:

 "A"   #: 6919333181322027406
 L"B"  #: 11959850520494268278
 u8"C" #: 12432341034569643010
 u"D"  #: 312659256970442235
 U"E"  #: 18073225910249204957
 Arcturus Vega Capella Rigel

.SH See also

   hash    hash function object
   \fI(C++11)\fP \fI(class template)\fP

   std::hash<std::basic_string> hash support for strings
   \fI(C++11)\fP                      \fI(class template specialization)\fP
